Re: [PATCH 1/6] KVM: SEV: Disallow COPY_ENC_CONTEXT_FROM if target has created vCPUs

[Peter Gonda]

On Tue, Nov 9, 2021 at 2:53 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> Reject COPY_ENC_CONTEXT_FROM if the destination VM has created vCPUs.
> KVM relies on SEV activation to occur before vCPUs are created, e.g. to
> set VMCB flags and intercepts correctly.
>
> Fixes: 54526d1fd593 ("KVM: x86: Support KVM VMs sharing SEV context")
> Cc: stable@xxxxxxxxxxxxxxx
> Cc: Peter Gonda <pgonda@xxxxxxxxxx>
> Cc: Marc Orr <marcorr@xxxxxxxxxx>
> Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
> Cc: Nathan Tempelman <natet@xxxxxxxxxx>
> Cc: Brijesh Singh <brijesh.singh@xxxxxxx>
> Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
>  arch/x86/kvm/svm/sev.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 3e2769855e51..eeec499e4372 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -1775,7 +1775,12 @@ int svm_vm_copy_asid_from(struct kvm *kvm, unsigned int source_fd)
>         mutex_unlock(&source_kvm->lock);
>         mutex_lock(&kvm->lock);
>
> -       if (sev_guest(kvm)) {
> +       /*
> +        * Disallow out-of-band SEV/SEV-ES init if the target is already an
> +        * SEV guest, or if vCPUs have been created.  KVM relies on vCPUs being
> +        * created after SEV/SEV-ES initialization, e.g. to init intercepts.
> +        */
> +       if (sev_guest(kvm) || kvm->created_vcpus) {
>                 ret = -EINVAL;
>                 goto e_mirror_unlock;
>         }

Now that we have some framework for running SEV related selftests, do
you mind adding a regression test for this change?

> --
> 2.34.0.rc0.344.g81b53c2807-goog
>